Air-core coil and manufacturing method thereof

ABSTRACT

The present invention provides an air-core coil  21  wherein one conductor is wound into a spiral form to thereby form consecutively, axially of the coil, a plurality of unit turn portions ( 25, 26, 27 ) which are different from each other in inner peripheral length and to form, axially of the coil, unit coil portions comprising the plurality of unit turn portions ( 25, 26, 27 ) to produce a partly finished coil  20 , and thereafter the partly finished coil  20  is compressed to force the unit turn portion of small inner peripheral length inwardly of the unit turn portion of great inner peripheral length from among the unit turn portions providing each of the unit coil portions to thereby make each of the unit coil portions multi-layered. Thus the air-core coil  21  exhibits a smaller voltage across layers than conventionally and excellent frequency characteristics.

TECHNICAL FIELD

The present invention relates to coils to be provided in rectifiercircuits, noise eliminating circuits, resonance circuits, etc. for usein various AC devices, and a process for fabricating the coils.

BACKGROUND ART

Conventionally known is a coil device of the troidal type, whichcomprises an air-core coil 81 fitted around a bobbin 10, as shown inFIG. 11. The air-core coil 81 is fabricated, for example, by winding aconductor around an outer surface of a wire winding jig (not shown) inthe order indicated by the numerals of 1 to 29 as shown in the drawing.First the conductor is wound around the outer surface of the jig in theorder of 1 to 10 to form a first layer 82, thereafter the conductor iswound around the outer surface of the first layer 82 in the order of 11to 19 to form a second layer 83, and finally the conductor is woundaround the outer surface of the second layer 83 in the order of 20 to 29to form a third layer 84, to thereby fabricate the air-core coil 81having three layers.

With the air-core coil 81 shown in FIG. 11, however, the first layer 82,the second layer 83 and the third layer 84 are lapped over as connectedto each other in series. This results in the appearance of a straycapacity between each pair of turns of the conductor adjacent to eachother axially of the coil and the appearance of a stray capacity betweeneach pair of turns of the conductor lapped over in a directionorthogonal to an axis of the coil, as shown in FIG. 12. In this case thenumber 1 turn in the first layer 82 and the number 19 turn in the secondlayer 83 are lapped over each other, and the number 11 turn in thesecond layer 83 and the number 29 turn in the third layer 84 are lappedover each other, thus rendering high a potential difference between theturns lapped over each other, i.e., voltage across the layers, as shownin FIG. 12. This gives rise to the problem of the voltage resistance ofthe air-core coil 81. Furthermore there is also the problem of impairedfrequency characteristics of the air-core coil 81 due to the increasedstray capacity.

The present applicant has proposed the process shown in FIGS. 13(a) and13(b) for fabricating a coil device which comprises a coil fitted arounda core (see the publication of JP-A No. 2000-277337). According to thisfabrication process, a coil device as shown in FIG. 13(b) is fabricatedby inserting one side portion of an air-core coil 8 into a center hole70 of a C-shaped core 7 through a gap portion 71 thereof as shown inFIG. 13(a) and fitting the coil 8 around the core 7. With thisfabrication process, the air-core coil 8 separated from the core 7 ismade, and the coil 8 is thereafter fitted around the core 7 to completethe coil device. The process is therefore simplified by eliminating theneed to wind a wire around the core 7 and making the air-core coil 8automatically.

In fabricating the conventional coil device shown in FIGS. 13(a) and13(b), a rectangular conductor or trapezoidal conductor can be used asthe conductor of the air-core coil in order to increase the ratio of thesectional area of the turns of conductor 9 passing through the centerhole 70 of the core 7, to the total area of the center hole 70, i.e.,the space factor of the conductor 9. When having the same crosssectional area as a round conductor, the rectangular conductor andtrapezoidal conductor have a short side which is smaller than thediameter of the round conductor, so that an increased number of turns ofconductor can then be accommodated in the center hole 70 of the core 7,hence a higher space factor. However, the rectangular or trapezoidalconductor has the problem of being more expensive than the roundconductor.

Another process for fabricating a coil device of higher space factor isknown which comprises winding a conductor 9 around a core 7 in the orderindicated by the numerals of 1 to 13 in FIG. 14(a), and thereafterwinding the conductor 9 around the core 7 in the order indicated by thenumerals of 14 to 23 in FIG. 14(b) so as to provide one coil layer onthe outer peripheral side of the core 7 and two coil layers on the innerperipheral side of the core 7. An increased number of turns of conductorcan then be accommodated in the center hole 70 of the core 7 to resultin a higher space factor. The conductor 9 is nevertheless difficult towind around the core 7 automatically and must be wound by manual work,which involves the problem of low production efficiency.

Accordingly, an object of the present invention is to provide anair-core coil which has a lower voltage across the layers thanconventionally and improved frequency characteristics and which canachieve a high space factor without using a rectangular or trapezoidalconductor, and a process for fabricating the air-core coil which processcan be practiced automatically.

DISCLOSURE OF THE INVENTION

The present invention provides an air-core coil comprising unit coilportions each having at least one conductor wound into a spiral form,the unit coil portions being arranged repeatedly axially of the coil,each of the unit coil portions comprising a plurality of unit turnportions which are different from each other in inner peripheral length,the unit turn portion of small inner peripheral length being at leastpartly forced inwardly of the unit turn portion of great innerperipheral length.

Stated specifically, the plurality of unit turn portions providing eachof the unit coil portions are sequentially wound from an innerperipheral side to an outer peripheral side, or from the outerperipheral side to the inner peripheral side. One unit turn portion onan outermost periphery or on an innermost periphery is connected toanother unit turn portion on an outermost periphery or on an innermostperiphery of the adjacent unit coil portion.

With the air-core coil of the present invention, the plurality of unitturn portions providing each of the unit coil portions are lapped overin a direction intersecting the axis of the coil. These unit turnportions are sequentially formed by winding one continuous conductor.The winding numbers are consecutive, so that a stray capacity betweenturns is small. Furthermore, with each pair of unit coil portionsadjacent to each other, a plurality of unit turn portions are lappedover axially of the coil. Each pair of the unit coil potions adjacent toeach other is sequentially formed by the one continuous conductor, torender relatively small the stray capacity between turns.

According to a process for fabricating the air-core coil of the presentinvention, a plurality of unit turn portions which are different fromeach other in inner peripheral length are consecutively formed axiallyof the coil, and the unit coil portions comprising the unit turnportions are repeatedly formed axially of the coil, by winding at leastone conductor into a spiral form, to produce a partly finished air-corecoil, and the unit turn portions of small inner peripheral length arethereafter at least partly forced inwardly of the unit turn portions ofgreat inner peripheral length from among the unit turn portionsproviding each of the unit coils by compressing the partly finished coilaxially of the coil, whereby each of the unit coil portions is made atleast partly multi-layered.

According to the fabrication process, the partly finished air-core coilcan be fabricated with ease by winding one conductor into a spiral formwhile varying the inner peripheral length, because with the partlyfinished air-core coil having arranged axially of the coil a pluralityof unit turn portions which are different in inner peripheral length,the conductor forming the unit turn portions is not lapped over in adirection orthogonal to an axis of the coil (in a direction of windingdiameter). The partly finished air-core coil thus obtained is merelycompressed axially of the coil to thereby obtain the air-core coil ofthe present invention described.

Stated specifically, the partly finished coil is fabricated by windingthe conductor around an outer peripheral surface of a wire wiring jig.The wire wiring jig comprises a plurality of winding cores arrangedaxially of the coil. Each pair of the winding cores adjacent to eachother differs in outer peripheral length. The unit turn portion of smallinner peripheral length is formed by winding the conductor around thewiring core of small outer peripheral length of the jig. The unit turnportion of great inner peripheral length is formed by winding theconductor around the wiring core of great outer peripheral length of thejig.

According to the specific construction, the partly finished coilcomprising a plurality of turn portions of varied inner peripherallengths can be fabricated with ease by winding the conductor around thejig. Accordingly the fabrication process can be automated.

As described above, the air-core coil of the present invention exhibitsa smaller stray capacity between the turns of the conductor thanconventionally, resulting in reduced voltage between the layers, toobtain an excellent voltage resistance and improved frequencycharacteristics. Furthermore, the coil device including the air-corecoil of the present invention can achieve high space factor irrespectiveof the type of conductor used. The air-core coil fabricating process ofthe present invention can be practiced automatically.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an air-core coil embodying the presentinvention;

FIG. 2 is a sectional view of the air-core coil;

FIG. 3 is an equivalent circuit diagram of the air-core coil;

FIG. 4 is a perspective view of a wire wiring jig;

FIG. 5 is a perspective view of a stepped member;

FIG. 6(a) is a plan view of the stepped member;

FIG. 6(b) is a side elevation of the stepped member;

FIG. 7(a) is a perspective view of a partly finished coil;

FIG. 7(b) is a sectional view of the partly finished coil;

FIG. 8(a) is a perspective view of the partly finished coil as viewedfrom a direction different from FIG. 7(a);

FIG. 8(b) is a sectional view of the partly finished coil as viewed froma direction different from FIG. 7(b);

FIGS. 9(a) and 9(b) are sectional views illustrating a compressing stepof the partly finished coil;

FIGS. 10(a) and 10(b) are sectional views illustrating a compressingstep of the partly finished coil as seen from a direction different fromFIGS. 9(a) and 9(b);

FIG. 11 is a sectional view of the conventional air-core coil;

FIG. 12 is an equivalent circuit diagram of the air-core coil;

FIGS. 13(a) and 13(b) include diagrams showing a step included in aconventional process for fabricating a choke coil;

FIGS. 14(a) and 14(b) include diagrams showing steps included in anotherconventional process for fabricating a choke coil.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will be described below in detailwith reference to the drawings.

FIGS. 1 and 2 show the construction of an air-core coil 21 embodying theinvention. The air-core coil 21 comprises a conductor 91 fitted aroundan outer surface of a bobbin 10, and has a layer-structure comprising afirst layer 21 a, second layer 21 b and third layer 21 c according to anexample illustrated.

The air-core coil 21 is provided by winding one conductor therearound inthe order indicated by the numerals 1 to 29 shown in FIG. 2. Unit coilportions are each provided by turns of consecutive numerals (1 to 3), (4to 6), . . . , (25 to 27) and (28 to 29). The unit coil portions arearranged into ten rows axially of the coil.

Each of the unit coil portions comprises a unit turn portion having thegreatest inner peripheral length, a unit turn portion having the mediuminner peripheral length, and a unit turn portion having the smallestinner peripheral length, each of which has one turn of a conductor. Theunit coil portions of the medium inner peripheral length are forcedinwardly of the unit coil portions of the greatest inner peripherallength. The unit coil portions of the smallest inner peripheral lengthare further forced inwardly of the unit coil portions of the mediuminner peripheral length. With the unit coil portion provided by turns ofwinding numbers 1 to 3, for example, the unit turn portion of windingnumber 2 is forced inwardly of the unit turn portion of winding number3, and the unit turn portion of winding number 1 is forced inwardly ofthe unit turn portion of winding number 2.

Accordingly, the air-core coil 21 shown in FIG. 2 has alternatelyarranged axially of the coil, unit coil portions each comprising threeunit turn portions wound sequentially from the inner peripheral side tothe outer peripheral side, and unit coil portions each comprising threeunit turn portions wound sequentially from the outer peripheral side tothe inner peripheral side. The unit turn portion on the outermostperiphery or on the innermost periphery of each of the unit coilportions is connected to the unit turn portion on the outermostperiphery or on the innermost periphery of the adjacent unit coilportion.

With the air-core coil 21 of the present invention, the conductor 91 iswound as layered in a direction orthogonal to an axis of the coil toform the unit coil portion while the unit coil portion is repeatedlyformed axially of the coil, so that each pair of the turns adjacent toeach other has a close winding number. For example, the unit turnportion of the number 4 and the unit turn portion of the number 9 areadjacent to each other, and the difference in the number between the twounit turn portions is only five. Accordingly, as shown in FIG. 3, astray capacity rarely appears between each pair of turns adjacent toeach other in a direction orthogonal to an axis of the coil. A straycapacity between each pair of turns adjacent to each other axially ofthe coil is extremely small. Consequently a potential difference V2(voltage across the layers) between each pair of turns adjacent to eachother becomes sufficiently low, improving a voltage resistance of theair-core coil 21. Furthermore the small stray capacity improvesfrequency characteristics of the air-core coil 21.

For example, when the voltage across terminals of the coil is 200 V andthe number of turns is 29 turns, the voltage per turn is approximately6.9 V. With the conventional air-core coil 81 shown in FIG. 11, thevoltage V1 across the unit turn portion of the winding number 1 and theunit turn portion of the winding number 19 is 6.9 V×18=124.2 V. On theother hand, with the air-core coil 21 of the present invention shown inFIG. 2, the voltage V2 across the unit turn portion of the windingnumber 1 and the unit turn portion of the winding number 6 is 6.9V×5=34.5 V which is one-third of the conventional value. The voltageresistance of the coils matters particularly when an abnormal voltage isapplied thereon, so that the air-core coil 21 of the present inventionis made highly reliable.

FIG. 4 shows a wire winding jig 51 for use in fabricating the air-corecoil 81 of the present invention. The wire winding jig 51 comprises aflat plate member 52 and stepped members 53 removably fixed to oppositeend portions of opposite surfaces of the flat plate member 52,respectively. As shown in FIG. 5, FIGS. 6(a) and 6(b), the steppedmembers 53 are formed by repeating an arrangement cycle comprising alow-level stepped portion 55, medium-level stepped portion 56,high-level stepped portion 57, medium-level stepped portion 56, andlow-level stepped portion 55. Incidentally FIG. 6(a) is a plan view ofthe stepped member 53. FIG. 6(b) is a side elevation of the steppedmember 53. Each stepped portion of the stepped members 53 is given thenumerals 1 to 29 indicating the order when the conductor is wound.

FIGS. 7(a) and 7(b), and FIGS. 8(a) and 8(b) are views of a partlyfinished coil 20 comprising a conductor 91 wound around the wire windingjig 51 and as viewed from a 180 degree-different direction.

Winding the conductor 91 starts with the low-level stepped portion 55positioned on the end portion of the wire wiring jig 51 shown in FIG. 4,and proceeds sequentially to the medium level stepped portion 56, thehigh level stepped portion 57, the medium level stepped portion 56, andthen the low level stepped portion 55. Incidentally whereas the lowlevel stepped portion 55 and the medium level stepped portion 56 eachhas a width for winding the conductor 91 only one turn, the high levelstepped portion 57 has a width for winding the conductor 91 two turns.

A first unit turn portion 25 having the smallest inner peripheral lengthis formed by winding the conductor 91 around the low level steppedportion 55. A second unit turn portion 26 having the medium innerperipheral length is formed by winding the conductor 91 around themedium level stepped portion 56. A third unit turn portion 27 having thegreatest inner peripheral length is formed by winding the conductor 91around the high level stepped portion 57. In these steps, as shown inFIGS. 7(a) and 7(b), when wiring the conductor proceeds from one steppedportion to the adjacent stepped portion of the wire winding jig 51, theconductor 91 moves therebetween as stretched in an oblique direction onone side surface of the wire wiring jig 51. Incidentally, as shown inFIGS. 8(a) and 8(b), the conductor 91 is straightened between the samelevel stepped portions on the other side surface of the wire wiring jig51.

After the conductor 91 has been wound around the wire wiring jig 51 therequired number of turns, the wire wiring jig 51 is disassembled tothereby obtain a partly finished coil 20 shown in FIG. 7(a) and FIG.8(a). The partly finished coil 20 is thereafter compressed axially ofthe coil, as shown in FIG. 9(a) and FIG. 10(a), to thereby force thesecond unit turn portion 26 inwardly of the third unit turn portion 27,and to force the first unit turn portion 25 inwardly of the second unitturn portion 26, as shown in FIG. 9(b) and FIG. 10(b), whereby theair-core coil 21 having three layers can be obtained.

The air-core coil 21 having three layers shown in FIG. 9(b) and FIG.10(b) involves an elastic repulsive force for stretching axially of thecoil. The elastic repulsive force of the air-core coil 21 is, however,received by the bobbin 10 with the air-core coil 21 fitted around thebobbin 10 as shown in FIG. 1, maintaining the three-layer coilstructure. Alternatively, the three-layer coil structure can also bemaintained by wrapping with tape the air-core coil 21 having threelayers and shown in FIG. 9(b) and FIG. 10(b).

According to the air-core coil 21 fabricating process as described, theair-core coil 21 of the present invention can be fabricated merely bymaking the partly finished coil 20 shown in FIG. 9(a) and FIG. 10(a)with the wire wiring jig 51 shown in FIG. 4, FIG. 5, FIG. 6(a), and FIG.6(b), and thereafter compressing the partly finished coil 20 axially ofthe coil, as shown in FIG. 9(b) and FIG. 10(b). Thus the fabricationprocess can be automated with ease, and further the air-core coil 21without losing its coil shape and as wound neatly in order can beobtained.

The device of the present invention is not limited to the foregoingembodiment in construction but can be modified variously within thetechnical scope set forth in the appended claims. For example, thestructure of the air-core coil 21 is not limited to the three-layerstructure, but the air-core coil 21 can be made into two-layer structureor four-or-more-layer structure. Furthermore, the wire wiring jig 51shown in FIG. 4 is not limited in configuration to the one included inthe above embodiment, but jigs of various shapes are usable insofar asair-core coils can be made wherein adjacent unit coil portions aredifferent in inner peripheral length.

Furthermore, the conductor 91 forming the air-core coil 21 is notlimited to a single wire like the conductor used in the foregoingembodiment but can be a plurality of wires. The conductor 91 is notfurther limited to the round conductor having a circular cross section,but can be a rectangular conductor having a rectangular cross section.

1. An air-core coil comprising unit coil portions each having at leastone conductor wound into a spiral form, the unit coil portions beingarranged repeatedly axially of the coil, each of the unit coil portionscomprising a plurality of unit turn portions which are different fromeach other in inner peripheral length, the unit turn portions of smallinner peripheral length being at least partly forced inwardly of theunit turn portions of great inner peripheral length.
 2. An air-core coilaccording to claim 1 wherein the plurality of unit turn portionsproviding each of the unit coil portions are sequentially wound from aninner peripheral side to an outer peripheral side, or from the outerperipheral side to the inner peripheral side, one unit turn portion onan outermost periphery or on an innermost periphery being connected toanother unit turn portion on an outermost periphery or on an innermostperiphery of the adjacent unit coil portion.
 3. An air-core coil whereina plurality of unit turn portions which are different from each other ininner peripheral length are consecutively formed axially of the coil,unit coil portions comprising the unit turn portions being repeatedlyformed axially of the coil, by winding at least one conductor into aspiral form, to produce a partly finished air-core coil, and thereafterthe partly finished coil is compressed axially of the coil to therebyforce the unit turn portion of small inner peripheral length at leastpartly inwardly of the unit turn portion of great inner peripherallength from among the unit turn portions providing each of the unit coilportions, whereby each of the unit coil portions is made at least partlymulti-layered.
 4. A coil device comprising an air-core coil fittedaround a core or a bobbin, the air core coil comprising unit coilportions each having at least one conductor wound into a spiral form,the unit coil portions being arranged repeatedly axially of the coil,each of the unit coil portions comprising a plurality of unit turnportions which are different from each other in inner peripheral length,and the unit turn portions of small inner peripheral length being atleast partly forced inwardly of the unit turn portions of great innerperipheral length.
 5. A coil device according to claim 4 wherein theair-core coil includes the plurality of unit turn portions providingeach of the unit coil portions, the unit turn portions beingsequentially wound from an inner peripheral side to an outer peripheralside, or from the outer peripheral side to the inner peripheral side,one unit turn portion on an outermost periphery or on an innermostperiphery being connected to another unit turn portion on an outermostperiphery or on an innermost periphery of the adjacent unit coilportion.
 6. A coil device comprising an air-core coil fitted around acore or a bobbin, the air core coil wherein a plurality of unit turnportions which are different from each other in inner peripheral lengthare consecutively formed axially of the coil, unit coil portionscomprising the unit turn portions being repeatedly formed axially of thecoil, by winding at least one conductor into a spiral form, to produce apartly finished air-core coil, and thereafter the partly finished coilis compressed axially of the coil to thereby force the unit turn portionof small inner peripheral length at least partly inwardly of the unitturn portion of great inner peripheral length from among the unit turnportions providing each of the unit coil portions, whereby each of theunit coil portions is made at least partly multi-layered.
 7. A processfor fabricating an air-core coil comprising winding at least oneconductor into a spiral form to thereby form, axially of the coil,consecutively a plurality of unit turn portions which are different fromeach other in inner peripheral length and to repeatedly form, axially ofthe coil, unit coil portions comprising the unit turn portions tothereby produce a partly finished air-core coil, and compressing,axially of the coil, the partly finished coil to thereby force the unitturn portions of small inner peripheral length at least partly inwardlyof the unit turn portions of great inner peripheral length from amongthe unit turn portions providing each of the unit coil portions, therebymaking each of the unit coil portions at least partly multi-layered. 8.A process for fabricating an air-core coil according to claim 7 whereinthe partly finished coil is fabricated by winding the conductor aroundan outer peripheral surface of a wire wiring jig, the wire wiring jigcomprising a plurality of winding cores arranged axially of the coil,each pair of the adjacent winding cores being different from each otherin outer peripheral length, the unit turn portion of small innerperipheral length being formed by winding the conductor around thewiring core of small outer peripheral length of the jig, the unit turnportion of great inner peripheral length being formed by winding theconductor around the wiring core of great outer peripheral length of thejig.